FLAGSTAFF, Ariz. — Sen. John McCain said Friday that he considers the death of American Kayla Mueller by Islamic State militants one of the saddest moments of his life as he looked back on his work in trying to secure her freedom and the government’s policy of not paying ransom to terrorists.

McCain discussed the Mueller saga during a news conference in Phoenix a week after confirmation of Mueller’s death. McCain, himself a prisoner of war during the Vietnam War, worked to get Mueller set free over the last 18 months after she was captured in Syria in August 2013. At one point, the Islamic State group demanded money for her release, but the U.S. has a policy of not paying ransom in hostage situations.

“It’s a very tough issue. Your head tells you one thing, and your heart tells you something else. Your heart tells you that you want to do anything, anything to bring someone like Kayla Mueller home,” he said. “At the same time, any outside objective expert will testify that when we ransom people like that, then it encourages more hostage-taking. So it’s a very, very tough issue, and unfortunately, after a lot of thought, I have agreed that I don’t think it’s a good idea to ransom hostages.”

The confirmation of Mueller’s death this week galvanized President Barack Obama’s efforts to attack Islamic State.